Graphite rheostat



(No Model.)

E. W. JEWELL. GRAPHITE RHEOSTAT.

Patented Janfll lll lllllllllllll UNITED STATES PATENT EEicE.

EDIVARD W. JEVELL, OF CHICAGO, ILLINOIS.

GRAPHITE. RHEOST'I.

SPECIFICATION forming part of Letters Patent No. 597,002, dated January11, 1898.

Application led May 8,1897. Serial No. 635,658. (No model.)

To @ZZ whom t may concern:

Be it known that I, EDWARD XV. J EwELL, a citizen of the United States,residing at Ohicago, in the county of Oook and State of Illinois, haveinvented a certain new and useful Improvement in Graphite Rheostats,(Oase No. 1,) of Which the following is a full, clear, concise, andexact description, reference being had to the accompanying drawings,forming a part of this specification.

My invention relates to rheostats; and I have found it to be 0f specialvalue in electro therapeutic operations, where a very gentle and gradualvariation of current in the working circuit is essential.

The resistance material which I employ is graphite evenly distributedupon an insulating-base, preferably of stone or slate. This resistance,of uniform cross-sectional area at all points, is introduced in shunt tothe operating-circuit, one of whose terminals consists of a suitablecontact-arm arranged to make a iirin electrical connection with any partof the graphite resistance, the other terminal being at one end of theresistance.

In accordance with the law of divided circuits the Voltage in theoperating-circuit will vary directly with the increase or decrease ofresistance in the shunt as the contact-arm is moved along the graphite,thus producing what may be termed a 4uniformly-graded7 resistance.

By this construction I am enabled to secure insensible variations inVoltage, it being possible te change from the full strength of eurrentdown to zero in a perfectly uniform ratio with no sudden jerks which areunpleasant and injuriousin medical treatment, and which have been almostimpossible to avoid heretofore.

It has been impossible heretofore to construct a rheostat forelectroinedical work in which the variations in voltage could be made sogradual as to be insensible to the patient, especially in connectionwith dental surgery. It has been proposed to introduce a resistance ofgradually-increasing cross-section in series with the operating-circuit.This, however,

has been found inefficient, because it is extremely difficult to startor regulate the current by means of such a rhecstat without causing aperceptible jerk in the current, and consequently intense pain to thepatient.

By the use of my invention these harmful effects are avoided, and instarting a current, especially the increase from absolute Zero to anyrequired strength, is made in a perfectly uniform gradation, as amovement of the contact-arm through a given distance along any portionof the surface of the graphite will always change the Voltage in theexact ratio in which such distance is proportioned to the total lengthof the graphite path.

My invention has been especially successful in operations ofelectrolysis and electric diffusion as performed in dental surgery,where the utmost care is necessary to prevent sudden changes in thestrength of the current.

A further feature of my invention consists 7 in an improved binding-postwhich will permit the connection of a second conductor without in anywaydisturbing a connection already made. I find this especially useful, forinstance, in connecting a voltmeter across 7 the circ uit withoutdisturbing the connections or operation of apparatus which may beincluded between the same two binding-posts.

My invention further contemplates an improved and novel method ofmaintaining a 8 good electrical connection between the graphite and theconductor, attached thereto.

rIhe accompanying drawings will assist in explaining the operation of myinvention.

Figure l is a plan View, the electrical con- 8 nections being indicatedlin dotted lines. Fig. 2 is a sectional view taken along the line 2 2 ofFig. l. Fig. 3 is a detail view of the improved binding-post of myinvention. Fig.

4: illustrates a screw provided with a conical 9 washer of soft metal,which I employ in electrically connecting a conductor with the graphiteresistance.

Like letters are used to designate like parts in all figures. 9

The graphite resistance c is applied uniformly to a raised portion h' ofthe slate base h. In the center of the base is pivoted an arm c,provided with metallic contact-springs c c', which are maintained infirm sliding engagement with the surface of the graphite. rIhe handle c2may be grasped to rotate the con IOO tact-arm. The binding-posts P and Nare for connection with the positive and negative terminals of thebattery or other source of current. Conductor d serves to connect thepost P with one end of the graphite resistance at the point af, whileconductor e similarly connects post N with the other end of theresistance at the point y. Binding-posts P P and N N are respectivelythe positive and negative terminals of the working or patients circuit,a conductor f connecting post P l) with the contact-arm o and conductorg eX- tending from the post N N to the point where conductor e is unitedwith the end of the graphite resistance. Current entering at l will flowfrom the point agthrou gh the graphite a, to the point 1y, going ont bythe post N. ln this distinct circuit ior the current it will meet with auniformly graded resistance, preferably of several thousand ohms.lletween the points .t and 1/ there will be a difference of potentialcorresponding to the electromotive force of the current, with a uniformdrop in that potential all along the line. Thus if the rheostat is usedon a twenty-volt circuit the difference of potential between the middlepoint of the rheostat and the point jz/ will be ten volts, while at thepoints S and S2 it will be live volts and fifteen volts, respectively.lf the contact-arm be placed at the point 'y and rotated in a clockwisedirection, the difference of potential between the posts P P and N Nwill rise very gently and gradually from zero to the full twenty voltswhen it reaches the point a'. The voltage in the patients circuit thusdepends upon the relative position of the contact-arm upon the graphitesurface.

lVith the use of my invention current may safely and advantageouslyT betaken from an ordinary one-huiidred-and-ten-volt in candescent-lightingcircuit even for the most delicate electrotherapeutic operations.

The screws t' 'L' t" t, which are used to make connection between thegraphite resistance and the plates L 7e', to which conductors aresoldered, are preferably provi-ded with conical washers of soft metal,such as block-tin. The graphite is firmly packed about the sides of thecountersunk holes, in which the screwheads rest. The conical block-tinwashers Z are interposed between the screw-heads and the graphite, sothat when a nut is tightened upon the shank of a screw the washer isslightly expanded and forced into very lirm rengagement with thegraphite. More graphite is then tamped into the countersunk hole tocover the head of the screw, and the union is complete. 'Conductorswhich it is desired to electrically connect with the graphite arepreferably soldered to one of the plates 7.: 7d, according to which endof the graphite is to be connected.

The binding-post illustrated in Fig. 3 of the J drawings l lind to be avery valuable accessory. lt has two points of advantage over theordinary variety in that the binding-nut 7L may not be wholly removedand lost from the threaded stem L/ of the post, the outer end ol saidstem being enlarged to retain the nut. The threaded stem or shank isalso hollow to aiford an auxiliary socket or seat for an auxiliaryswitch pin or plug, which may be inserted therein. l find it desirableto make permanent connections7 so to speak, by means ol' theplug-and-socket device,when other connections may readily be made in theusual manner by the threaded bin ding-nut 7L without in any wisedisturbing the lirst circuit. This mode of connection is most desirable,for it is essential in medical treatment, as l have before stated, toavoid suddenly making or breaking a circuit and also to avoid suddenchanges of resistance in the working circuit due to loose or imperfectconnections. Binding-posts such l have described readily permit changesof connection without suddenly breaking or altering the condition of thecircuit.

It is evident, of course, that the use of my invention is not restrictedto electromedical work. ln fact, l have found it very desirable as aiield-rheostat for dynamo-electric machines.

Having described my invention, what l claim as new, and desire to secureby Letters Patent, is-

l. In a rheostat, the combination with an insulating-base, of auniformly-gradcd graphite resistance mounted thereon, a contact-armadapted to travel over and make lirm electrical connection with saidgraphite resist-- ance, binding-posts P N in electrical connection witheach end of said gra `phite resistance, binding-posts P P and N N inelectrical connection with the said contact-arm and one end of saidgraphite resistance respectively, and auxiliary sockets in said bindingposts adapted to receive independent s vitch plugs or connectors,substantially and for the purpose described.

2. ln a rheostat, the combina-tion with a uniformly-graded graphiteresistance in shunt with the workin g circuit, a contact-arm adapted totravel over said graphite resistance and forming one terminal of saidworking circuit, binding-posts for making suitable connce tions, andauxiliary sockets in said bindingposts adapted to receive switch plugser pins, independent of such connections, substantially as described.

3. The combination with the base h, of a screw having an enlargedconical head, a countersunk portion in said base adapted to receive saidscrew-head, graphite applied to the sides of said countersnnk portion,and a conical soft-metal washer interposed between the screw-head andgraphite, substantially as and for the purpose specified.

Ll. ln a binding-post, the combination with the threaded shank, of athreaded nut therefor, and an enlargement upon the end of said shank toprevent the total removal of said n ut, substantially as described,

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5. In a binding-post, the combination with the threaded shank, of athreaded bindingnut therefor, and a socket or seat in said shank adaptedto receive a switch pin or plug, substantially as an d for the purposespecied.

G. In an electrotherapeutic apparatus, the combination with a working orpatients circuit forming one distinct path for the electric current, ofa thin layer of graphite evenly distributed upon an insulating-baseforming a second path of high resistance for the cur rent, a contact-armarranged to travel along said graphite layer and make electrical contacttherewith, the cross-sectional area of said graphite path beingsubstantially equal at all points of adjustment of said arm, an elec-

